There has been conventionally known a method of connecting electric wires, including a step for stripping off coatings of a plurality of insulated electric wires thereby to expose conductors, and a step for welding the exposed conductors together by ultrasonic welding (For example, Patent Document 1). According to this method of connecting electric wires, it is possible to enhance connecting strength, because the conductors of a plurality of the insulated electric wires are twisted together in the same direction, and then, welded by ultrasonic welding.